This invention relates to a yoke for coupling helicopter blades to a mast; and more particularly, the invention relates to a coupling system characterized by a long oval loop of glass fibers embedded in a cured adhesive to form a solid oval loop having side portions which are reinforced for withstanding torque transmitted from the mast to the blades.
Helicopter rotor blades have been coupled by many different structures to a rotating mast for the transfer of torque from a rotor to the blades. Representative of mounting structures for two bladed teetering rotors is the yoke disclosed in U.S. Pat. No. 3,652,185 and a similar yoke disclosed in U.S. Pat. No. 3,804,552. Such yokes are characterized by a flat metal plate oriented generally perpendicular to the axis of the mast and secured through a pivotal mounting to the mast. The plate is resilient so that it forms a virtual hinge to accommodate the flapping forces that may be encountered.
The highly desirable properties of fiber glass, particularly the fatigue strength thereof, and other composite materials makes the use of such materials desirable in enhancing the useful life of helicopter rotor systems where they are subject to high and repeated stresses. The problem of coupling an all composite fiber glass yoke to the mast for transfer of torque has been a significant deterrent to achieving this end. The present invention, however, is directed to a structure which satisfies the operational requirements and provides for the torque transfer in a manner that lends to long yoke life.